Based on the discovery of the inherent capacity of SNARES to fuse membranes, now demonstrated for mammalian exocytic, yeast ER- Golgi, and yeast vacuolar SNARES, the overall goal of the proposed research is to test directly and comprehensively whether SNARE-dependent fusion is a general principle in biology (aims 1- 6) and the extent to which compartmental specificity is encoded in SNARE proteins (aim 7). We will capitalize on the completion of the yeast genome to enable these fundamental questions for cell biology to be addressed in a single cell type which will also be extensively harnessed to provide critical genetic tests of the physiological relevance of the findings from biochemistry (aim 8). It is now within our reach to completely characterize the binding interactions and fusogenic capacity of every SNARE protein in the yeast cell, and this is indeed our intent. The process of vesicular transport is of basic importance to biology and medicine, underlying the compartmental organization of the cytoplasm and the pathways of exocrine, endocrine, and neurosecretion. Knowledge of the mechanism of action of gene products in these pathways, and their allelic variants, will likely be important for predictive medicine and impact upon management of common diseases such as cancer, diabetes, cardiovascular disease and diseases of the central nervous system.